Use Nemeth Indicators to Delimit Math Content in Text

## MathCAT Version

MathCAT-0.6.6 (NVDA Add-On)

## Current Behavior

When MathCAT encounters in-line math content and is set to render math as Nemeth, it inserts one space before the math and two spaces afterward to distinguish it from the surrounding text.

## Proposed Change

[Nemeth indicators](https://nemeth.aphtech.org/lesson3.8) would likely serve as better delimiters. Benefits include

+ a more natural rendering of mixed content (text interspersed with math), since that is how such content would be brailled physically.
+ more conspicuous indication of code switching (especially useful in STEM documents).
+ easier identification of symbols (e.g., punctuation) directly following math content, as the Nemeth indicators occupy the full height of the cells they use.
+ the ability (at least in theory) to use NVDA's braille output as (nearly) embosser-ready Unicode braille (since the standard is to use Nemeth indicators in UEB documents with Nemeth math content).

Perhaps an option could be given to toggle this behavior if desired.

## Comparison

### Mixed-Content Statement

In this case, $y$ is proportional to $x^2$.

### Current Nemeth Output (Unicode)

⠠⠔⠀⠹⠀⠉⠁⠎⠑⠂⠀⠀⠰⠽⠀⠀⠀⠊⠎⠀⠏⠗⠕⠏⠕⠗⠰⠝⠁⠇⠀⠞⠕⠀⠀⠭⠘⠆⠀⠀⠲

### Proposed Nemeth Output (Unicode)

⠠⠔⠀⠹⠀⠉⠁⠎⠑⠂⠀⠸⠩⠀⠽⠀⠸⠱⠀⠊⠎⠀⠏⠗⠕⠏⠕⠗⠰⠝⠁⠇⠀⠞⠕⠀⠸⠩⠀⠭⠘⠆⠀⠸⠱⠲

If Nemeth indicators were adopted, then the grade 1 symbol indicator would not be necessary before the $y$.

首先追蹤 MathCAT 繪製 Nemeth 時 NVDA Add-On 如何處理行內數學，然後將目前的間距與此 issue 中提出的指示符序列進行比較。完成應意味著混合文字和數學使用指定的 Nemeth 分隔符，並且行為以及任何可選的 Toggle 都已得到明確解決。

由索引模型根據 Issue 內容生成。